Modern processes for manufacturing semiconductor devices require precise adjustment of many process parameters to achieve high levels of device performance, product yield, and overall product quality. For processes that include the formation of semiconductive layers on substrates with epitaxial film growth, numerous process parameters have to be carefully controlled, including the substrate temperature, the pressures and flow rates precursor materials, the formation time, and the distribution of power among the heating elements surrounding the substrate, among other process parameters.
Current trends in CMOS technology are favoring processes that can produce increasingly thin layers (e.g., dielectric layers only 60–80 Å thick or less), and films with increasing complexity. For example, conventional BiCMOS devices, using single-element silicon (Si) films, are being displaced by two-element, silicon-germanium (SiGe) films that have superior qualities in logic and DRAM devices. As the sizes of these devices continue to shrink, the uniformity of the film thickness and composition across the substrate becomes increasingly important. Maintaining a high level of uniformity is made even more challenging due to the increasing sizes of the substrates, with the standard substrate wafer diameter moving from 200 mm to 300 mm, and beyond.
In many conventional semiconductor manufacturing process, including epitaxial film growth processes (“EPI processes”), process parameters can be manually adjusted to make films with the requisite uniformity of film thickness and composition. In EPI processes for making alloy films (e.g., SiGe films), especially doped alloy films, the sensitivity of several process parameters on film quality is increased, making it more difficult to tune these parameters by hand. The increased sensitivity makes manual control of semiconductor film growth processes much more difficult, if not impossible.
There is also increasing complexity in the relationship between process parameters and the qualities of the manufactured film layer. Increasingly, the interdependences of multiple process parameters on a property of the layer make it more difficult to find optimum values for the parameters to achieve a target value for the property. For example, in an EPI process trying to achieve a target thickness uniformity of a film layer across the substrate, the interdependences of the power ratios between inner/outer and upper/lower substrate heating elements have to be understood. Only with this understanding can the process operator set the parameters to values that result in a sufficiently uniform thickness of the deposited layer. Moreover, the interdependence of the parameters make determining the parameter values much more difficult than if the effects of each parameter on thickness uniformity were completely independent.
Thus, there is a need for systems and methods of tuning process parameters in semiconductor film growth processes that reduce or eliminate the manual adjustment of the process parameters. There is also a need for systems and methods to determine values of interdependent process parameters for making a film layer with the desired properties. These and other needs for semiconductor film making systems and processes are addressed by the present invention.